The present invention generally relates to a file data retrieving system, and in particular to a file data retrieving system which can be suitably applied to a microcomputer system having a data filing function, such as an electronic filing system and a work station. The present invention relates more particularly to a file data retrieving system capable of retrieving desired data at a high speed by displaying data read out from a file.
A conventional microcomputer system having a data filing function includes a central processing unit, a memory, a filing device, a compression and reproduction device, an interface circuit, a display unit, a keyboard and a character code generating and expanding circuit. Generally the filing device is constructed by a floppy disc, a hard disc, an optical disc or the like. Data to be filed is stored in the filing device as it is, or converted data is stored in order to save the memory capacity of the filing device. For example, a character code of data to be filed is stored as file data in the filing device. Also, image data derived from an optical scanner, for example, is compressed and is then stored as file data in the filing device.
In the above microcomputer system, various manners for retrieving a file and file data included in the file have been proposed. For example, a desired file can be found by referring to a title (file name) or subtitle given thereto. The file retrieval may be also carried out by reading out file data from the filing device and then displaying it on the display unit. An operator can check from the displayed file data as to whether the file being accessed is a desired one. Generally, file data is displayed per one page out of pages which make up one file. This type of the retrieval is also used to retrieve file data of a desired page on a desired file.
Displayed file data, or an image on one page can be produced from corresponding character codes in the case where character codes are stored as file data in the filing device. In the case where the compressed image data is stored as file data in the filing device, displayed file data are obtained by expanding the compressed image data so as to reproduce the original image data. If the operator needs a display of file data of a page subsequent to file data being displayed, a corresponding instruction is supplied to the data retrieving system. Then, the system starts producing the file data on the next page to be displayed in the manner described above. In this manner, the files stored in the filing device and file data included in the files can be retrieved.
However, the conventional file data retrieval system has a disadvantage that a long time is taken to retrieve file data. This is because a data process for reading out file data which is stored in the form of character codes or compressed image data and then reproducing the file data to be displayed is carried out independently per one page. That is, the file data on the next page to be displayed for retrieval is produced in the process identical to that for the proceeding page after the instruction for displaying the next page data is supplied to the system. The above problem is particularly evident for compressed image data obtained by a data compression process such as modified Huffman (MH) coding, modified READ coding and modified MR (M.sup.2 R) coding. That is, a very long time in the order of a few seconds is taken to expand the compressed image data to reproduce the original image data to be displayed. Therefore, the operator must wait for a few seconds for the display of the file data on the next page to be displayed. The above problem also causes a complicated file management.